Experts have slammed a team of scientists in China who claim to have altered the DNA of twins to grant them immunity to HIV, the AIDS virus.

Researchers from across the world have labelled the experiment 'irresponsible', with many calling into question the perverse moral and ethical implications.

One British scientist, who described the experiment as 'monstrous', said the researchers involved were playing 'genetic Russian Roulette' with healthy babies.

Gene editing is banned in Britain, the US many other parts of the world, largely because its long-term effects on mental and physical health are poorly understood.

The technique carries the risk that altered DNA will warp other genes - potentially dangerous mutations that may then be passed down to future generations.

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This graphic reveals how, theoretically, an embryo could be 'edited' using the powerful tool Crispr-Cas9 to defend humans against HIV infection

Experts have slammed a team of scientists in China who claim to have altered the DNA of twins to grant them immunity to HIV, the AIDS virus. In this image, Zhou Xiaoqin (left) and Qin Jinzhou, who worked on the experiment, prepare a tool for gene editing

Experts at China's Southern University of Science and Technology shocked the world Sunday night when they claimed to have successfully established a pregnancy from a gene-edited embryo.

The DNA of twin girls was altered with the powerful gene-editing tool CRISPR, project lead scientist Dr He Jiankui said.

He claimed the babies, named LuLu and Nana, were born a few weeks ago and have a resistance to infection with HIV, the AIDS virus.

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Scientists from institutions across the globe strongly condemned the experiment.

'If true, the report is very concerning,' said Dr Kathy Niakan of the Francis Crick Institute in London.

'This would be a highly irresponsible, unethical and dangerous use of genome editing technology.

He Jiankui speaks during an interview at a laboratory in Shenzhen in southern China's Guangdong province. The Chinese scientist claims he helped make world's first genetically edited babies: Twin girls whose DNA he claims to have altered

'Given the significant doubts about safety, including the potential for unintended harmful side-effects, it is simply far too premature to attempt this.'

Professor Julian Savulescu, Director of the University of Oxford's Uehiro Centre for Practical Ethics, said the experiment exposed healthy children to the risks of genetic engineering 'for no necessary benefit'.

'If true, this experiment is monstrous. These healthy babies are being used as genetic guinea pigs.

'This is genetic Russian Roulette.'

Zhou Xiaoqin removes the cryostorage sheath from a container for an embryo at Dr He's laboratory in Shenzhen in southern China's Guangdong province

WHAT ARE SOME OF THE DOUBTS SURROUNDING DR HE'S CLAIMS?

Several scientists reviewed materials that Dr He provided to the AP and said tests so far are insufficient to say the editing worked or to rule out harm.

They also noted evidence that the editing was incomplete and that at least one twin appears to be a patchwork of cells with various changes.

'It's almost like not editing at all' if only some of certain cells were altered, because HIV infection can still occur, famed Harvard University geneticist Professor George Church said.

Church and Dr Kiran Musunuru, a University of Pennsylvania gene editing expert, questioned the decision to allow one of the embryos to be used in a pregnancy attempt, because the Chinese researchers said they knew in advance that both copies of the intended gene had not been altered.

'In that child, there really was almost nothing to be gained in terms of protection against HIV and yet you're exposing that child to all the unknown safety risks,' Dr Musunuru said.

The use of that embryo suggests that the researchers' 'main emphasis was on testing editing rather than avoiding this disease,' Church said.

Even if editing worked perfectly, people without normal CCR5 genes face higher risks of getting certain other viruses, such as West Nile, and of dying from the flu.

Since there are many ways to prevent HIV infection and it's very treatable if it occurs, those other medical risks are a concern, Dr Musunuru said.

There also are questions about the way Dr He said he proceeded.

He gave official notice of his work long after he said he started it - on November 8, on a Chinese registry of clinical trials.

For example, consent forms called the project an 'AIDS vaccine development' program.

The hospital linked to the controversial project denied approving the procedure and accused Dr He of forgery.

This image shows a microplate containing embryos that have been injected with Cas9 protein using the controversial gene editing tool Crispr. The image was taken at Dr He's laboratory in Shenzhen last month

HOW DID DR HE DESCRIBE THE WORK?

'The gene editing occurred during IVF, or lab dish fertilisation.

'First, sperm was 'washed' to separate it from semen, the fluid where HIV can lurk.

'A single sperm was placed into a single egg to create an embryo.

'Then the gene editing tool was added.

'When the embryos were three to five days old, a few cells were removed and checked for editing.

'Couples could choose whether to use edited or unedited embryos for pregnancy attempts.

'In all, 16 of 22 embryos were edited, and 11 embryos were used in six implant attempts before the twin pregnancy was achieved.'

Some scientists called for the introduction of an international treaty on embryo research to halt similar experiments in future.

Professor Darren Griffin, at geneticist at the University of Kent, said: 'In a world where scientists, by and large, try to be aware of ethical and social issues surrounding the work that we do, this report takes us back to the Stone Age.

'Scientists cannot be seen to be trying to forge ahead in the absence of ethical constraint.

'An international treaty on embryo research is now an absolute priority to prevent this happening again.'

However, one famed geneticist, Harvard University's Professor George Church, defended attempting gene editing for HIV, which he called 'a major and growing public health threat.'

'I think this is justifiable,' Professor Church said of that goal.

Dr Jiankui, of the Southern University of Science and Technology, in Shenzhen, said he altered embryos for seven couples during fertility treatments, with one pregnancy resulting thus far.

He said his goal was not to cure or prevent an inherited disease, but to try to bestow a trait that few people naturally have - an ability to resist infection with HIV.

The DNA of twin girls was altered with a powerful new tool capable of rewriting the very blueprint of life, Chinenese researcher Dr He Jiankui says. Pictured id Dr He (left) with fellow researcher Zhou Xiaoqin at a laboratory in Shenzhen

He said the parents involved declined to be identified or interviewed, and would not say where they live or where the work was done.

There is no independent confirmation of Dr He's claim, and it has not been published in a journal, where it would be vetted by other experts.

He announced the research Monday in Hong Kong to an organiser of an international conference on gene editing that is set to begin Tuesday, and earlier in exclusive interviews with The Associated Press.

'I feel a strong responsibility that it's not just to make a first, but also make it an example,' he told the AP.

The researchers used a gene-editing tool called CRISPR-cas9 for their experiment, which makes it possible to operate on DNA. This image shows a video feed of a researcher in Dr He's team using the tool under a microscope

'Society will decide what to do next' in terms of allowing or forbidding such science.

In recent years scientists have discovered a relatively easy way to edit genes, the strands of DNA that govern the body.

The tool, called CRISPR-cas9, makes it possible to operate on DNA to supply a needed gene or disable one that's causing problems.

It's only recently been tried in adults to treat deadly diseases, with all edits confined to that person, meaning they cannot be passed down to their children.

Editing sperm, eggs or embryos is different - the changes can be inherited.

In this image an embryo is injected with proteins using the controversial Crispr-Cas9 technique

In the US, it's not allowed except for lab research. China outlaws human cloning but not specifically gene editing.

Some scientists were astounded to hear of the claim and strongly condemned it.

It's 'unconscionable ... an experiment on human beings that is not morally or ethically defensible,' said Dr Kiran Musunuru, a University of Pennsylvania gene editing expert and editor of a genetics journal.

'This is far too premature,' said Dr Eric Topol, who heads the Scripps Research Translational Institute in California. 'We're dealing with the operating instructions of a human being. It's a big deal.'

WHAT IS CRISPR-CAS9?

CRISPR-Cas9 is a tool for making precise edits in DNA, discovered in bacteria.

The technique involves a DNA cutting enzyme and a small tag which tells the enzyme where to cut.

The CRISPR/Cas9 technique uses tags which identify the location of the mutation, and an enzyme, which acts as tiny scissors, to cut DNA in a precise place, allowing small portions of a gene to be removed

By editing this tag, scientists are able to target the enzyme to specific regions of DNA and make precise cuts, wherever they like.

It has been used to 'silence' genes - effectively switching them off.

When cellular machinery repairs the DNA break, it removes a small snip of DNA.

In this way, researchers can precisely turn off specific genes in the genome.

The approach has been used previously to edit the HBB gene responsible for a condition called β-thalassaemia.